Three former Labour MPs and a Conservative peer face criminal trials over alleged expenses fraud after the Appeal Court ruled that parliamentary privilege could not protect them from prosecution.
David Chaytor, Elliot Morley, Jim Devine and Lord Hanningfield had argued that their cases should "lie within the hands of Parliament".
But Lord Judge, the Lord Chief Justice, and two other judges sitting in London, said they were "unable to envisage" how the ancient immunity could apply to dishonesty by parliamentarians.
The four men, who deny theft by false accounting, could mount a further challenge to this ruling in the Supreme Court, the highest court in the land.
Their case was that submitting an expenses claim was part of proceedings in Westminster and therefore protected by its parliamentary privilege.
But Lord Judge, sitting alongside the Master of the Rolls, Lord Neuberger, and Sir Anthony May, cited cases from as long ago as 1629 as he rejected their argument and upheld an earlier court ruling.
"It can confidently be stated that parliamentary privilege or immunity from criminal prosecution has never, ever attached to ordinary criminal activities by Members of Parliament," Lord Judge said.
"The stark reality is that the defendants are alleged to have taken advantage of the allowances scheme designed to enable them to perform their important public duties as Members of Parliament to commit crimes of dishonesty to which parliamentary immunity or privilege does not, has never, and, we believe, never would attach.
"If the allegations are proved, and we emphasise, if they are proved, then those against whom they are proved will have committed ordinary crimes."
Mr Chaytor, 60, of Todmorden, West Yorkshire, Mr Morley, 58, of Winterton, north Lincolnshire, Mr Devine, 57, of Bathgate, West Lothian, and Lord Hanningfield (also known as Paul White), 69, of West Hanningfield, Essex, are due to stand separate trials at Southwark Crown Court.